Black Sabbath's planned reunion for 2012 has been threatened by drummer Bill Ward.

Ward has revealed that he is not pleased with the proposed contract for the upcoming tour and album, and has refused to take part in further meetings with the band until the dispute is resolved.

"I am unable to continue unless a 'signable' contract is drawn up; a contract that reflects some dignity and respect toward me as an original member of the band," he wrote on his Facebook page.

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He added: "Several days ago, after nearly a year of trying to negotiate, another 'unsignable' contract was handed to me... The place I'm in feels lousy and lonely because as much as I want to play and participate, I also have to stand for something and not sign on.

"If I sign as-is, I stand to lose my rights, dignity and respectability as a rock musician. I believe in freedom and freedom of speech."

While he did not reveal the exact issues of the contract, he said that he "definitely want[s] to play on the album, and definitely want[s] to tour with Black Sabbath".

"My position is not greed-driven," he wrote. "I'm not holding out for a 'big piece' of the action like some kind of blackmail deal. I'd like something that recognises and is reflective of my contributions to the band."